1. Field of the Invention
This invention relates to harmonic drive transmissions, and more particularly to sensor driven actuator arrangements to improve the positional accuracy of harmonic drive systems.
2. Prior Art
Harmonic drive transmissions, sometimes known as controlled-ratio deflection type transmissions, are used where rotary to rotary transmission is needed. In such a transmission, the gear tooth engagement is induced at a plurality of points by the deflection of a thin ring gear or the like. The tooth engagement at a plurality of points around the circumference is propagated along the periphery of a thin ring gear as the crest of the induced deflection ring is made to move around this periphery. As the deflection moves around the gear, each tooth moves radially in and out of engagement as it progresses from one tooth to the next, tracing during this motion, a curve which is generally of the character of a sinusoidal wave, giving rise to the term "strain-wave gearing".
Examples of such early transmissions of this type are shown in U.S. Pat. No. 2,906,143, issued in 1959 to Musser, U.S. Pat. No. 2,931,249 issued to Musser, and U.S. Pat. No. 3,196,713 issued to Robinson, all of which are incorporated herein by reference.
Those transmission have found use in certain industries where rotary power is needed and increasingly so in the robotics industry. Such use, particularly in the robotics industry requires extreme accuracy. Heretofore, robotic transmissions and drive units have been empowered by direct drive motors which are able to repearably position the rotation of a shaft, within plus or minus 3 arc seconds. These motors typically are brushless and have a high output torque at a low velocity. Direct drive motors unfortunately are also very expensive.
It is an object of the present invention to provide a harmonic drive assembly, which may function as a direct drive motor replacement in the robotic industry.
It is yet a further object of the present invention, to provide a harmonic drive actuator arrangement, which permits highly accurate corrective positioning of the output shaft.
It is yet still a further object of the present invention to provide a harmonic drive apparatus with a sensor/encoder arrangement for speed and/or torque, position, vibration, temperature, performance degradation and/or tooth wear sensing utilizing self-diagnostic control of the apparatus.